In order to set a semiconductor integrated circuit into an electrically active state, it is necessary to anneal a semiconductor substrate having an integrated circuit arranged on the surface thereof at temperatures of 1000° C. or more. With recent miniaturization of a integrated circuit, it is increasingly required to greatly reduce the anneal time in comparison with the conventional case. With this trend, the technique of optical annealing for electrically activating a miniaturized circuit by illuminating light of high intensity onto the substrate surface is proposed. For example, flash lamp annealing (FLA) and laser spike annealing (LSA) are provided as representatives.
With the optical annealing technique, the illumination time is shorter than that in the case of annealing of several seconds such as spike rapid thermal annealing (RTA) that is the conventional technique and annealing of milliseconds is realized. Even if the illumination time of illumination light is several milliseconds, the surface temperature of the semiconductor substrate can be instantly raised to a high temperature and only the surface layer portion of the substrate can be annealed.
However, in the above optical annealing technique, the thermal diffusion time becomes shorter because of short-time illumination. Therefore, there occurs a problem that a temperature irregularity of 10° C. or more tends to occur in the scale of approximately 100 μm that is the thermal diffusion length. Since the temperature irregularity causes a variation in the threshold voltage or the like in the chip, it is necessary to suppress the temperature irregularity as far as possible. In order to cope with this, the technique for controlling the initial heating temperature before optical annealing for each wafer region, the technique for arranging a large number of lamps and thermometers to adjust light intensity and the like are considered.